Method for preventing caustic spray in electrochemical cleaning

ABSTRACT

Throwing of caustic solution into the air over electrochemical cleaning baths by evolved hydrogen is prevented by addition of trisodium hydroxyethylethylenediamine triacetate to the bath to form a blanket of foam on the bath during electrochemical cleaning operation.

nied States Patent [151 3,

Pollack et al. [451 an. 11; W7

[54] METHOD FOR PREVENTING cAusrlc 5,207,683 '9/1'96'5' Hermann ..204/145 SPRAY 1N ELECTROCHEMICAL 2,420,602 5/1947 Kingerley, Jr ..204/ 145 CLEANING Isidore Pollack, Westminister; Charles L. Dohogne, San Pedro, both of Calif.

Assignee: Purex Corporation, Ltd., Lakewood, Calif.

Filed: Oct. 15, 1969 Appl. No.: 866,728

Inventors:

US. Cl. ..204/141, 134/2, 204/145 R Int. Cl. .C23b l/04, C03c 23/00 Field of Search ..204/ 145, 141

References Cited UNITED STATES PATENTS Meyer ..i .Q 1 1647145 FOREIGN PATENTS OR APPLICATIONS 1,116,013 10/1961 Germany ..204/145 Primary Examiner-John H. Mack Assistant Examiner-T. Tufariello Attorney-White, Haefliger & Bachand [57] ABSTRACT 6 Claims, No Drawings of metal parts. Specifically the invention has to do with making such cleaning operations safer for operators by eliminating hazardous airborne caustic solution spray in the vicinity of the bath.

Electrochemical cleaning of metal parts is effected by immersing the part in a concentrated aqueous caustic solution and passing a current through the solution using the part as the cathode. The current evolves hydrogen at the part surface which is used to break obdurate scale from the part. This hydrogen then passes upwardly through the bath and ultimately rises from the bath surface, normally carrying with it small amounts of caustic. Caustic solution is of course highly hazardous as it may cause burns or blindness; The caustic aerosol also corrodes metals, removes paint and discolors wood in the bath area.

2. Prior Art Attempts to relieve the hydrogen evolution carryover of caustic from electrochemical cleaning baths is not satisfactorily solved by use of solid, e.g., metal covers impermeable to hydrogen, since dangerous concentrations of H may build up creating an explosion hazard SUMMARY OF THE lNVENTlON It has been discovered that trisodium hydroxyethylethylenediamine triacetate is unique among compounds in providing a foam blanket on a caustic electrochemical cleaning bath which prevents airborne spray of caustic above the bath to protect operators and property, but passes hydrogen gas sufficiently well to preclude buildup of dangerous concentrations of hydrogen at the bath surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To an electrochemical cleaning bath containing water and above about 40 percent by weight caustic, e.g., sodium hydroxide or potassium hydroxide e.g., 40 to 70 percent by weight of a mixture of sodium hydroxide and potassium hydroxide, a small, but effective amount of trisodium hydroxyethylethylenediamine triacetate is added. Ordinarily from 0.5 to 2 percent by weight based on the weight of the caustic in the bath will be used. One percent by weight of the trisodium hydroxyethylethylenediamine triacetate, same basis, is quite satisfactory.

The metal part to be cleaned is immersed in the bath and current is passed from an electrode (anode) in the bath to the metal part as cathode. Any current level providing hydrogen evolution at the metal part surface will be satisfactory, but current densities between about 0.5 and 2 amp/in. are generally employed. At these levels and with about one percent trisodium hydroxyethylethylenediamine triacetate based on the caustic weight, a foam about one-half inch thick forms over the top of the bath as the hydrogen is evolved to the surface. The hydrogen ultimately passes through the foam to the extent required to preclude explosive concentration of hydrogen between the foam blanket and the bath surface. On the other hand, any gas evolution from the bath is essentially caustic free and the formerly encountered spray of caustic from the bath is prevented by the foam blanket described. Desirably the foam blanket is between 0.25 and 1.0 inch thick with one-half inch being about optimum.

EXAMPLE A badly scaled aircraft engine part was immersed in a caustic bath containing a mixture of water and 70 percent by weight of equal parts of sodium hydroxide and potassium hydroxide. One percent by weight of trisodium hydroxyethylenediamine triacetate based on the weight of the mixture of hydroxides was added as a 50 percent aqueous solution. Current was assed through the bath to the art at l amp/in A foam b anket formed immediately, onealf inch thick on the top of the bath and no spray of caustic from the bath was encountered. The foam remained stable for a 1 hour use of the bath.

in a Control experiment, the tetrasodium salt of ethylenediamine tetraacetic acid was substituted in equal amount for the trisodium salt of the triacetic acid. No foam blanket formed and there was no preventing of caustic spray carryover from the bath.

Mixtures of l/ 10 and 10/1 of sodium and potassium hydroxide as well as either hydroxide alone may be used.

We claim:

1. In the method for electrocleaning metals in which the metal part to be cleaned is immersed in a caustic bath containing a mixture of water and above about 40 percent by weight caustic selected from sodium hydroxide and potassium hydroxide and mixtures thereof and electrical current is passed through the bath in a manner evolving hydrogen gas at the metal part in the bath which tends to carry aqueous caustic solution into the air above the bath, the step including forming a form layer over the top of the bath consisting essentially of water, hydrogen and a small but effective amount of trisodium hydroxyethylethylenediamine triacetate sufficient to form said foam layer.

2. Method according to claim 1 in which said bath contains from 40 to 70 percent by weight of a 10/1 to 1/10 mixture of sodium hydroxide and potassium hydroxide.

3'. Method according to claim 1 in which said trisodium hydroxyethylethylenediamine triacetate is present in an amount equal to 0.5 to 2 percent by weight of said caustic.

4. Method according to claim 1 in which said trisodium hydroxyethylethylenediamine triacetate is present in an amount providing a foam blanket from 0.25 to 1 inch thick on the bath which is hydrogen gas permeable.

5. Method according to claim 1 in which said bath consists essentially of water, 40 to 70 percent of a caustic mixture of equal parts by weight sodium hydroxide and 1 percent by weight trisodium hydroxyethylethylenediamine based on the caustic mixture.

6. Method according to claim 5 including passing 0.5 to 2 amps/in through the bath during cleaning.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,652,432 Dated March 28 1972 Inventor) Isidore Pollack and Charles L. Dohogne It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 36; "form" should read -foam singed and sealed this 15th day of August 1972.

(SEAL) Attest:

EDWARD M. FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC BOS'IG-PGQ h U.5. GDVERNMENY PRINYING OFFICE L 1959 O36G-334 FORM PO-105O (10-69) 

2. Method according to claim 1 in which said bath contains from 40 to 70 percent by weight of a 10/1 to 1/10 mixture of sodium hydroxide and potassium hydroxide.
 3. Method according to claim 1 in which said trisodium hydroxyethylethylenediamine triacetate is present in an amount equal to 0.5 to 2 percent by weight of said caustic.
 4. Method according to claim 1 in which said trisodium hydroxyethylethylenediamine triacetate is present in an amount providing a foam blanket from 0.25 to 1 inch thick on the bath which is hydrogen gas permeable.
 5. Method according to claim 1 in which said bath consists essentially of water, 40 to 70 percent of a caustic mixture of equal parts by weight sodium hydroxide and 1 percent by weight trisodium hydroxyethylethylenediamine based on the caustic mixture.
 6. Method according to claim 5 including passing 0.5 to 2 amps/in2 through the bath during cleaning. 